Process for stabilizing synthetic rubber



United States 3,406,146 PROCESS FOR STABILIZING SYNTHETIC RUBBER Kurt Ley and Wolfgang Redetzky, Leverknsen, Robert Seydel, Cologne-Dellbrueck, and Kurt Vohwinkel, Cologne-Stammheim, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany No Drawing. Filed June 30, 1965, Ser. No. 468,571 Claims priority, application Germany, July 2, 1964, F 43,329 9 Claims. (Cl. 26045.95)

ABSTRACT 'oF THE DISCLOSURE Synthetic rubber stabilized against cyclization by triarylphosphites wherein one or two of the aryl radicals contain a hydroxyl group.

phosphites or by reacting hydroxyphenyl dichlorophosphites with phenols.

Polybutadieneor butadiene-styrene copolymers are examples of synthetic elastomers which may be treated with the stabilizers to avoid cyclization. The stabilizers used according to the invention may be added in quantities of 0.1 to 5 parts by weight, preferably 0.5 to 1.5 parts by weight, based on 100 parts by weight of elastomer, and they may be added by the usual method on rollers or in internal mixers during hot mixing or before tempering. The stabilizers used according to the invention may also be added at an earlier stage, namely to the synthetic rubber latex (before it is 'worked up to the solid product), if desired together with other stabilizers.

When the stabilizers used according to the invention are added, the conditions for heat treatment of the synthetic rubber, e.g. hot rolling, hot mixing, tempering etc., may be more stringent Without cyclization of the rubber taking place. Better mechanical properties, e.g. higher tensile strength, higher elongation at break and less abrasion are thereby achieved in the vulcanizates. Other advantages are that when the process according to the invention is employed, the synthetic rubbers or batches of filler-rubber mixtures can be more easily worked up (i.e. they are of better plasticity) and the synthetic rubbers, batches and vulcanizates protected in this Way have better resistance to discolouration than those prepared with the compounds hitherto known.

The following examples illustrate the invention:

contain a hydroxyl group, in the synthetic rubber as a stabilizer.

TABLE 2 Without 2,2-methylene- Defo Hardness/ anticyclisation bis-(B-tertiary- Compound Compound Compound Compound Compound Compound Data Elasticity agent (for butyl-4-rnethyl- N o. 1 from No. 2 from N o. 3 from No. 4 from N o. 5 from N o. 6 from comparison) phenol) (for Table 1 Table 1 Table 1 Table 1 Table 1 Table 1 comparison) 10 minutes 1, 375/52 750/40 625/36 659/41 550/ 625/32 600/33 659/38 15 minutes l, 550/50 750/42 575/34 575/37 525/33 575/32 450/33 600/38 20 minutes 1, 900/56 675/44 500/32 550/39 500/32 500/34 500/33 650/40 30 minutes 2, 200/ 600/40 450/31 475/39 375/25 425/30 475/33 575/39 Colour of Brown Black brown Pale brown Pale brown Pale brown Pale brown Pale brown Pale brown polymer after 30 minutes hot rolling.

Examples of stabilizers which can be used are given in Example 1 Table 1.

50 The following mixture was rolled on a laboratory roll- TABLE 1 ing mill at a rolling temperature of 170 C.: Compound No. Chemical name Parts by weight (1) r [Bis-(3,5(di-tertiary butyl-4-hydroxyphenyl)-1- StYTFHe'PHtEEdEHB P Y 100 2 tp zg g llp q p g 14h dr h 1) 1 Anticychzation agent 1s-,-1-er1ar-u ox en Y fi i g& h l (Le. stablhzer) See Table 2 1 3 B 3,5-d'-t -t' b t -4- ox en -lif f ikfifi g1 fi g y) A sample was removed at the end of the tlme rndlcated [Bi$-(3,5Sii-telfiary-butyH-hydrqxyphenyl)'1- in each case and the Defo hardness and Defo elasticity (3,5 -d1methylphenyl)]-phosph1te. 5 [Bis-(3,5-di-tertiary-butyl-4-hydroxyphenyl)-1- e ermined according to DIN 53 514. The values obtained (4"-iso-dodecylphenyl)]-phosphite. (6) [(3,5 di temary buty1 4 hydmxyphenyn bis (4, n these tests are mmariz 1n T le 2. The number tertiary-butylphenyl)]-phosph1te.

before the stroke indicates the Defo hardness, that after the stroke the Defo elasticity. (DIN refers to the German Industrial Norm.)

Compound No. 3 in Table 1 was obtained as follows: 111 g. (0.5 mol) of 2,6-di-tertiary-butyl-hydroquinone were dissolved in 300 m1. of toluene. 62 g. (0.25 mol) 4 tertiary butylphenyl dichlorophosphite were added dropwise to this solution at 70 C. With stirring. Evolution of hydrogen chloride set in. The temperature was increased to C. and finally to C. and kept at that temperature until evolution of hydrogen chloride ceased. The toluene was withdrawn and g. of a yellow viscous oil remained behind.

3 Calculated for C H O P C, 74.0%; H, 8.1%; P,

mg no discolouration and 4 indicating a strong dis- 5 .03 Found: C, 73.5%; H, -8.7 P, 4.90% colouration.

TAB LE 3 0.5 part by 1.0 part by Weight/100 parts 0.5 part; by 0.5 part by Weight/100 parts 1.0 part by 1.0 part by by weight weight/100 parts weight/100 parts by Weight Weight/100 parts weight/100 parts ML-4/A-Mooney Without of rubber by weight by Weight of rubber by Weight by Weight value at 140 0. hot addition (for 2,2-methyleneof rubber of rubber 2,2'-methyleneof rubber of rubber air after comparison) bis-(6-tertiary- Compound Compound bis-(ti-tertiary- Compound Compound butyl-i-methyl- No. 3 from N0. 6 from butyl-4-methyl- No. 3 from No. 6 from phenol) (for Table 1 Table 1 phenol) (for Table 1 Table 1 comparison) comparison) hours 65/0 35/+5 36/+4 36/+5 39/+4 39/+5 39l+5 2 hours. 25/+4 24/+4 27/1-3 29/+4 Ell/+4 31/+4 3 hours 22/ 19/ +5 19/ +4 24/+4 24/+4 26/+3 4 hours.. 23/+5 2l/+4 12/+3 24/+4 iii/+4 27/+3 6 hours. 22/+5 /+5 Iii/+3 23/4-5 Iii/+4. 24/+4 Discoloration after 4 hours storage at 140 0. hot air 0 3 0 0 4 0 0 Compound No. 6 m Table 1 was prepared as follows: We claim:

222 g. (1 mol) 2,6-di-tertiary-butyl-hydroquinone were added portionwise to 900 g. of phosphorus trichloride and 1 g. of magnesium chloride. When evolution of hydrogen chloride had ceased, the reaction mixture was boiled for 4 hours and the excess of phosphorus trichloride distilled off. The oil remaining behind was diluted with 300 ml. of toluene. To this there were added 300 g. (2 mols) ptertiary-butylphenol and the mixture was heated until evolution of hydrogen chloride ceased. The magnesium chloride was filtered off and the toluene distilled oif. 530 g. of a colourless oil remained behind.

Calculated for C34H47O5P1I C, 72.4%; H, 8.3%; P, 5.48%. Found. C, 73.1%; H, 8.5%; P, 5.30%.

Example 2 In the following text, polybutadienes are understood to mean polymers which have been prepared by known methods by polymerization of butadiene using organemetallic compounds of the alkali metals or using organometallic mixed catalysts in organic solvents. Homopolymers of butadiene for which the particulars given below are applicable can also be prepared with radical catalysts in emulsion.

32 liters of butadiene in 230 liters of toluene were polymerized under the usual conditions for polymerization with organometallic mixed catalysts, using a catalyst mixture of 74.5 g. of aluminum triisobutyl, 29.1 g. of titanium butoxytriiodide and 11.0 g. of titanium tetrachloride at temperatures between 0 and 20 C. After 2.2 hours, the yield was 96%.

The polymer solution was pumped into a vessel equipped with a stirrer, which vessel'contained 0.2 kg. of disproportionated resinic acid and the quantities indicated below of the various stabilizers dissolved in 5 liters of toluene. The solvent was then removed by steam distillation and the rubber lumps obtained dried in an expander screw. 20 kg. of polybutadiene having a Mooney viscosity of ML-4=48 were obtained.

The stability was tested by storing the product for varying lengths of time in hot air at 140 C. and then measuring the Mooney viscosity ML-4 according to DIN 53 523. A satisfactorily stabilized polybutadiene shows a slight drop in the Mooney viscosity; the shape of the Mooney curve obtained by the difference in the Mooney viscosity (A-Mooney value after 1 minute and 4 minutes) is also good measure of the stability. The A-Mooney value should have a positive sign and be as high as possible. The results obtained with different doses of stabilizers are indicated in Table 3. The resulting discolouration is indicated by the number 0 to 4, 0 indicat- 1. A composition of matter comprising synthetic diene rubber stabilized against cyclization by from 0.1 to 1.5 parts by weight, based on parts by weight of synthetic rubber of a triaryl phosphite of the formula wherein R and R stand for an alkyl radical having 4 to 7 carbon atoms, the carbon atom adjacent to the phenyl radical being a tertiary carbon atom, R stands for an alkyl radical having up to 12 carbon atoms and It stands for 1 or 2.

2. The composition according to claim 1 wherein the triarylphosphite is [Bis-(3,5-cli-tertiary-butyl-4-hydroxyphenyl) -1- (phenyl) ]-phosphite.

3. The composition according to claim 1 wherein the triarylphosphite is [Bis-(3,S-di-tertiary-butyl-4-hydroxyphenyl -1-(4-methylphenyl) ]-phosphite.

4. The composition according to claim 1 wherein the triarylphosphite is [Bis-(3,S-di-tertiary-butyl-4-hydroxyphenyl) -1- (4'-tertiary-butylphenyl) -phosphite.

5. The composition according to claim 1 wherein the triarylphosphite is [Bis-(3,5-di-tertiary-butyl-4-hydroxyphenyl -l (3,5 '-dime'thylphenyl) 1-phosphite.

6. The composition according to claim 1 wherein the triarylphosphite is [Bis-(3,5-di-tertiary-butyl-4-hydroxyphenyl)-1-(4'-iso-dodecylphenyl) ]-phosphite.

7. The composition according to claim 1 wherein the triarylphosphite is [(3,5 di tertiary butyl 4 hydroxyphenyl) -bis-(4-tertiary-butylphenyl) -phosphite.

8. The composition according to claim 1 wherein the diene rubber is a styrene-butadiene polymer.

9. The composition according to claim 2 wherein the diene rubber is a styrene-butadiene polymer.

References Cited UNITED STATES PATENTS 3,039,993 6/ 1962 Friedman 260-45] 3,080,338 5/1963 Nudenberg et 'al. 260-45.7 3,112,286 11/1963 Morris et a1 26045.95 3,244,661 4/1966 Kline 26045.7 3,061,583 IO/1962 Huhn et a]. 26045.7

DONALD E. CZAJA, Primary Examiner.

H. A. LAYLER, Assistant Examiner. 

